Three-phase transformer having four core legs



July 30, 1968 D. s. STEPHENS 3,395,373

THREE-PHASE TRANSFORMER HAVING FOUR CORE LEGS Filed Aug. 51, 1966 2 Sheets-Sheet 1 ATTORNEY July 30, 1968 D. s. STEPHENS 3,395,373

THREE-PHASE TRANSFORMER HAVING FOUR CORE LEGS Filed Aug. 31. 1966 2 Sheets-sheet z FIG-3.

64 7o T Tf TT" 1* 1 FIGA.

United States Patent O 3,395,373 THREE-PHASE TRANSFORMER HAVING FOUR CORE LEGS Donald S. Stephens, Sharpsville, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 31, 1966, Ser. No. 576,370 7 Claims. (Cl. 336-12) ABSTRACT 0F THE DISCLOSURE A three-phase transformer having first, second and third wound type magnetic core sections, each having two leg portions. The three magnetic core sections are disposed adjacent one another to provide first, second, third and fourth winding legs. The second and third winding legs include leg portions from the rst and second magnetic core sections, and the second and third magnetic core sections, respectively. The first and fourth winding legs are single leg portions from the first and third magnetic core sections, respectively. First, seco-nd, third and fourth winding sections are disposed in inductive relation with the first, second, third and fourth winding legs, respectively, with the second and third winding sections each forming a phase of the three-phase transformer, and with the first and .fourth winding sections being serially connected to provide the third phase.

This invention relates in general to electrical inductive apparatus, such as transformers, and more particularly to winding and magnetic core structures for polyphase electrical inductive apparatus.

Three-phase transformers having wound-type magnetic cores have been used for many years. One of the reasons they have not been completely replaced by stacked type polyphase magnetic cores, is the fact that the size of the wound-type polyphase cores may be easily and inexpensively changed, compared with the cost of new punchingV dies for obtaining new lamination sizes for polyphase stacked type cores.

The conventional three-phase wound-type magnetic core, however, has certain disadvantages. The fact that it has three single-phase type co-re sections does not facilitate the manufacture of the core. In fact, the necessary mechanical interdependence of the three single-phase type core sections greatly multiplies the manufacturing problems. For example, two similar single-phase type wound sections must first be wound upon separate mandrels. Then, these two magnetic core sections, along with their mandrels, are disposed on a face plate, and the third magnetic core section is wound about the rst two magnetic core sections, This forms a very awkward structure, which must be removed from the winding machine and blocked to shape. Each of the magnetic core sections must then be cut to form two matching halves, in order to facilitate assembly with its associated electrical windings. The cut ends o-f the matching halves are ground and etched, and the sections are then reassembled and banded in conjunction with the electrical windings. The close tolerances between the vario-us magnetic core sections, necessary in order to reduce core losses to a minimum, creates manufacturing problems related to maintaining dimensional accuracy. Also, the -bauding of the three-phase wound-type 3,395,373 Patented July 30, 1968 ice core does not force the inner legs of the core tightly together; in fact, the banding tends to distort the core.

In addition` tol the hereinbefore mentioned mechanical and manufacturing problems, the resulting structure is not magnetically balanced, as the end or outer legs do not have equal reluctance through the other two legs.

Accordingly, it is an object o-f the invention to provide a new and improved three-phase transformer having a wound-type magnetic core.

A yfurther object of the invention is to provide a new and improved three-phase transformer having a woundtype magnetic core structure formed of three similar single-phase type core sections each having substantially the same dimensions, and which are not mechanically interdependent.

Another object of the invention is to` provide a new and improved three-phase transformer having a wound-type magnetic core struct-ure which requires less magnetic material than similarly rated structures of the prior art.

Still another object of the invention is to provide a new and improved three-phase transformer having a woundtype magnetic core structure which has three similar single phase type core sections which may be separately banded.

Another object of the invention is to provide a new and impro-ved three-phase transformer having a woundtype magnetic core structure which has a substantially balanced magnetic circuit.

Another object yof the invention is to provide a new and improved three-phase transformer having a woundtype magnetic core structure which is easier to manufacture than certain wound-type polyphase magnetic core structures of the prior art.

Briefly, the present invention accomplishes the above cited objects by providing a three-phase transformer having a new and improved three-phase magnetic core and winding structure which requires the use of three singlephase type magnetic core sections. The three single-phase magneti-c core sections have similar dimensions, and are disposed adjacent one another to form two winding legs which are made up of the legs of two adjacent core section-s, and two winding legs each of which is a leg of a single core section, having one half the cross sectional area of one of the other legs. First, second, third and fourth winding structures o-r sections are provided, each having primary and secondary coils. The primary coils and the secondary coils of each of the winding structures have a like number of turns, respectively, with the second and third winding structures being dimensioned to encircle the winding legs formed by the two adjacent magnetic core sections, and the first and fourth winding structures being dimensioned to encircle the remaining winding legs, formed by the single magnetic core structures. The second and third winding structures form two of the three phases of the transformer. The primary coils and the secondary coils of `the first and lfourth winding structures are serially connected, respectively, to form the third phase of the transformer. Thus, three similarly dimensioned single-phase type cores, which have no critical interrelated dimensions, are utilized to provide a new and improved three-phase transformer structure lwhich requires less magnetic core material than certain threephase wound-type magnetic core structures of the prior art, and which has a substantially balanced magnetic circuit.

Further objects and advantages of the invention will become apparent from the following detailed description, taken in connection with the accompanying drawings, in which:

FIGURE `l is an elevational view of a three-phase transformer having a woundetype magnetic core structure and associated windings constructed according to the teachings of the invention;

FIG. 2 is a plan view of the three-phase transformer structure shown in FIG. 1, which includes a schematic diagram illustrating how the windings may lbe connected;

FIG. 3 is an elevational View of sa three-phase transformer constructed according to another embodiment of the invention; and

FIG. 4 is a plan view of the transformer construction shown in FIG. 3.

Referring now to the drawings, and FIG. 1 in particular, there is shown an elevational view, partially cut away, and partially in phantom, of a three-phase transformer constructed according to the teachings of the invention. Transformer 10 includes a core-coil assembly 12, disposed in a suitable casing or tank 14, which is shown cut away in order to more clearly illustrate the core-coil assembly 12. The core-coil assembly 12 includes a magnetic core structure 16, and a winding structure 18, which is shown in phantom in-FIG. l to more clearly illustrate the magnetic core structure 16.

Magnetic core structure 16 includes three single-phase type magnetic core sections 20, 22, and 24, which have similar dimensions. Each of the magnetic core sections is of the wound type, being formed of a strip of metallic, magnetic material, such as singly or multiply oriented silicon steel, which is wound upon a mandrel to provide a predetermined number of nested or superposed lamination turns 26. Each magnetic core section has an opening or winding window 28 for receiving its 4associated winding, a predetermined radial build made up of the plurality of nested lamination turns, a depth determined by the strip width, and the core sections are shaped to provide two winding legs, and two connecting yoke por-tions. For example, magnetic core lsection 20 has winding legs and 32, and yoke portions 34 and 36; magnetic core section 22 has winding leg portions 38 and 40; and yoke portions 42 and 44; and, magnetic core section 24 has winding leg portions 46 and 48, and yoke portions 50 and 52.

Each of the magnetic core sections may have an openable joint, such as the butt-type joint 54 in leg 30, and the butt-type joint 56 in leg 32, of magnetic core section 20, in order to Ifacilitate the Iassembly of the winding structure 18 with the magnetic core sec-tions. Thus, using butt-type joints 54 and 56, each magnetic core section is divided into two type C cores, which are held together by suitable banding means (not shown).

The assembly of the magnetic core sections to form magnetic core assembly 16 requires only that the core sections 20, 22 and 24 be disposed in side-by-side relation, with their leg portions adjacent to one another. For example, as shown in the embodiment illustrated in FIG. 1, the outer lamination turns of the Various leg portions are disposed adjacent to and in substantially contacting relation with one another, forming a magnetic core assembly 16 in which the various magnetic core sections are disposed in a common plane. Thus, two inner and two outer winding legs are formed, with the end or outer winding legs being similar in cross section, and comprising leg portion 30 of magnetic core section 20 and leg portion 48 of magnetic core section 24. The two inner winding leg portions are formed by the two adjacent leg portions of magnetic core sections 20 and 22, and the two adjacent leg portions of magnetic core sections 22 and 24, with leg portions 32 and 38 forming a single winding leg 60, and leg portions and 46 forming a single winding leg 62. Winding legs 60 and 62 therefore, have twice the cross sec-tional area of Winding legs 30 and 48.

In describing the winding structure 18, which is shown in phantom in FIGURE 1, FIG. 2 will also be referred to, which is a plan view of the transformer 10 shown in FIG. 1, and which illustrates the winding structure 18 in full. Winding structure 18 includes four lwinding sections 64, 66, 68 .and 70, disposed in inductive relation with winding legs 30, 60, 62 and 48, respectively.

Winding section 66 includes primary and secondary coils 72 and `74, respectively, as shown in FIG. 2, each having a predetermined number of conductor turns, which forms one of the phases of transformer 10. In like manner, winding section 68 includes primary and secondary coils 76 and 78, respectively, each having the same number of conductor turns as the primary and secondary coils, respectively, of winding section 66, with winding section 68 forming another of the phases of transformer 10. Since winding sections 66 and `68 have the same number of conductor turns and since they both encircle the winding leg having substantially the same cross sectional configuration and area, winding sections 66 and 68 are similar in size, weight and appearance.

The remaining phase of three-phase transformer 10 ncludes both winding sections 64 and 70. Winding section 64 includes primary and secondary coils 80 and 82, respectively, and winding section 70 includes primary and secondary coils 84 and 86, respectively, as shown in FIG. 2. The primary coils and 84 of winding sections 64 and 70 are serially connected, and the secondary coils 82 and 86 of winding sections 64 and 70 are serially connected, as will hereinafter be described.

Since winding sections 64 and 70 encircle winding legs 30 and 48, respectively, which have one half the cross sectional area of winding legs 60 and 62, the primary coils 80 and 84 each require the same number of conductor turns as each of the primary coils 72 and 76 of winding sections 66 and 68, land the secondary coils 82 and 86 each require the same number of conductor turns as each of the secondary coils 74 and 78 of winding sections 66 and 68. Winding sections `64 and 70, each have the same number of conductor turns, and each encircle a winding leg of substantially same cross sec-tional configuration and area, and thus are similar in size, weight and appearance to one another.

Winding `sections 64 and 70, having the same number of conductor turns as winding sections 66 and 68, will have the same radial build dimension, but will have a shorter mea-n turn length due to the smaller cross sectional area of their associated winding legs.

As shown in FIG. 2, each of the primary and secondary coils of each of the Winding sections have two leads, which connect to opposite ends of the coils, respectively. Winding section `64 has leads 94 and 96 connected to primary coil 80 and leads 98 and 100 connected to secondary coil 82; winding section 66 has leads 102 and 104 connected to primary coil 72, and leads 106 and 108 connected to secondary coil 74; winding section 68 has leads 110 and 112 connected to primary coil 76 and leads 114 and 116`connected to secondary coil 78; and, winding section 70 has leads 118 and 120 connected to primary coil 84 and leads 122 and 124 connected to secondary coil 86.

As herein'before stated, the primary coils `80 .and 82 of winding sections 64 and 70 are serially connected, as shown by conductor 90, and the secondary coils 82 andl 86 of winding sections 64 and 70 are serially connected, as shown 'by conductor 92, with the serially connected primary and secondary coils forming one of the winding phases of transformer 10. The primary and secondary coils may `be connected in any desired three-phase configuration. For purposes of example, primary coils 72, 76 and the serially connected primary coils 80` and 84, are shown connected in delta, with leads 104 and 110 being connected together via conductor 126, leads 94 and 112 Abeing connected together via conductor 128, and leads 102 and 120 being connected together via conductor 130. Conductors i, 126 and 128 'are connected to line terminals 1312, 134 and 136, respectively.

Also, for purposes of example, secondary coils 74 and 78, and the serially connected secondary coils 82 and 86, are shown connected in wye, with leads 98, 106 and 114 being connected together via conductor 148, and to neutral terminal 142, and leads 108, 116 and 124 being connected to terminals 144, 146 and 148, respectively.

Thus, the three-phase transformer construction shown in FIGS. 1 and 2 utilizes three singleJp-hase type wound magnetic core sections, all having substantially the same dimensions, and vmechanically related `such that there are no critical dimensions relative to one another. In addition rto the elimination of the magnetic core section which encircles two other magnetic core sections, a construction commonly used in the prior art three-phase wound core configuration, `the magnetic core structure taught by the invention requires only 75% of the corematerial of said prior art wound core structures. Although the inven-tion does require one more winding section than threephase transformers of the prior art, since two of the winding sections are smaller than the 4conventional winding sections, the extra weight and material required by the -additional winding section is more than offset by the advantages -realized by the teachings of the invention. For example, in addition to the savings in core weight, and elimination of 4certain manufacturing problems due to the absence of interrelated dimensions of the core sections and the relatively simple structures of thecore sections, the transformer shown in FIGS. 1 and 2 has the advantages of placing positive pressure on the core joints by the individual banding means associated with each of the magnetic core sections, and the three phase magnetic circuit shown in FIGS. 1 and 2 is substantially balanced, as the reluctance from any one winding leg through the remaining legs is substantially the same for all winding legs.

A 3 kva. three-phase transformer was constructed according to the teachings of the invention, and the weight of the core .and copper, as well as the core losses of the transformer, are listed in Table I las transformer type A. F or comparision purposes, similar data for similarly rated prior art .three-phase transformers having wound-type cores is listed under transformer types B and C in Table I. Transformer type B is of the type hereinbefore described, in which two similar wound sections .are enclosed within a larger wound section. Transformer type C is a threephase arrangement constructed of three single phase transformers. The weight saving-s Irealized by ,the teachings of the invention results in a cost savings of about the same ratio.

TABLE I Transformer Type Total Active Weight 30. 9 34. 3 44.1 No Load Core Loss (watts) 21. 5 26. 4 30. 0 Exclting Volt Amperes 134 110 150 The overall length of transformer 10 may be reduced by the width of two of the leg portions of the magnetic core sections, vby offsetting or overlapping the magnetic core sections as shown in FIGS. 3 and 4. Like reference numerals in FIGS. 1, 2, 3 and 4 indicate like components.

More specifically, instead of aligning the magnetic core sections 20, 22 and 24 into a single plane, in which the outer tum laminations of the legs are disposed adjacent one another, magnetic core sections 20 and 24 may -be disposed such that their leg portions 32, Iand 46 overlapI the leg portions 38 and 40 of magnetic core section 22. In other words, the edges of the lamination turns of the core sections of the adjacent leg portions substantially a'but one another to form winding legs `60 and 62. In this instance, it may be desirable to form the magnetic core sections 20, 22 and 24 of doubly oriented magnetic strip material, having a first direction of preferred magnetic grain orientation parallel with the edges of the magnetic strip, and a second direction of preferred magnetic grain orientation perpendicular to the edges of the magnetic strip, in order to reduce core losses.

Winding sections 464 and 7l), disposed about the end winding legs 38 and 48, will be the same as in the embodiment of the invention shown in FIGS. 1 and 2. Winding sections 66 and 68', however, are given prime marks to indicate that their window or opening dimensions may not be the same as in the embodiment shown in FIGS. 1 and 2. Although each embodiment would have the same cross sectional area of corel material contained within the windings, the length and width dimensions of the opening may differ, depending upon the core build or sta-ck height and width of the magnetic strip used in winding the `core sections.

Magnetic core sections 20, 2.2 and 24 are illustrated in FIGS. 3 with a stepped-lap type joint for opening the core sections, such as stepped lap joint shown in magnetic core section 20, to illustrate that other types of openable joints, other than the lbut-type joints shown in FIG. 1 may be used.

Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in :the accompanying drawings, shall be interpreted as illustrative, and not in a limiting sense.

I claim as my invention:

1. A three-phase transformer comprising first, second and third wound-type magnetic core sections, each having two leg portions, said first, second and third wound-type magnetic core sections being disposed adjacent one another to provide first, second, third and fourth winding legs, said second and third winding legs including leg portions of said first and second magnetic core sections, and said second and third magnetic core sections, respectively, and said first and fourth winding legs including the remaining leg portions of said first and third magnetic core sections, respectively,

first, second, third and fourth winding sections disposed in inductive relation with said first, second, third and fourth winding legs, respectively, said second and third winding sections each forming a phase of the three-phase transformer,

said first and fourth winding sections being serially connected to form the third phase of the three-phase transformer.

2. The three-phase transformer of claim 1 wherein said first, second and third wound-type magnetic core sections each have substantially the same dimensions.

3. The three-phase transformer of claim 1 wherein said first and fourth winding sections have substantially the same dimensions, and said second and third winding sections have substantially the same dimensions, which are different from the dimensions of said first and fourth winding sections.

4. The three-phase transformer of claim 1 wherein each of said first, second, third and -fourth winding sections have substantially the same number of conductor turns.

5. The three-phase transformer of claim 1 wherein each of said first, second, third and fourth winding sections have primary and secondary coils, with the primary coils having substantially the same number of conductor turns, and the secondary coils having substantially the sarne number of conductor turns, and with the primary coils and the secondary coils of said first and fourth winding sections being serially connected, respectively.

6. The three-phase transformer of claim 1 wherein the References Cited outer lamination turns of the wlndmg legs of sald rst, second :and third Wound-type magnetic core sections are UNITED STATES PATENTS disposed in adjacent, substantially contacting relation to 2,991,437 7/ 1961 Kreuzer et al. 336-215 form said second and third winding legs.

7. The three-phase transformer of claim 1 wherein FOREIGN PATFNTS the edges of the lamination turns of the Winding legs of 583,957 1947 Great Bmam' said first, second and third wound-type magnetic core I l sections are disposed in adjacent relation to `form said LARAMIE EASKINPHmwy Examme" Second and third Winding legs, l0 T. I. KOZMA, ASSSCIII Examl'lr. 

